There are various known types of voltage regulators for power management systems, including both linear regulators and switch mode regulators. One particularly useful type of linear voltage regulator is referred to as a low dropout (LDO) voltage regulator. LDO regulators can operate correctly even when the input voltage is only about one volt higher than the regulated output voltage, and thus LDO regulators are particularly useful for high efficiency power management systems like battery operated devices. A typical LDO regulator includes a voltage reference such as a bandgap voltage reference circuit, an error amplifier, and an output voltage divider. The error amplifier changes the output voltage to make the divided output voltage equal to the reference voltage, and typically includes a pass transistor between the input and output voltage terminals.
Bandgap voltage reference circuits provide stable references but require substantial integrated circuit area. However simpler voltage reference circuits tend to have poor power supply rejection ratio (PSRR). Moreover the resistors used by the output voltage divider to form the divided output voltage create noise, which appears in the regulated output voltage. What is needed then is a low-cost, low-noise LDO regulator with high PSRR.
The use of the same reference symbols in different drawings indicates similar or identical items.